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package org.example.jdbc;import java.sql.*;public class FirstExample {    static final String JDBC_DRIVER = "com.mysql.jdbc.Driver";    static final String DB_URL = "jdbc:mysql://127.0.0.1:3306/test?useUnicode=true&characterEncoding=utf-8&useSSL=false&serverTimezone=CTT";    static final String USER = "root";    static final String PASS = "jianan";    public static void main(String[] args) {        Connection conn = null;        Statement stmt = null;        ResultSet rs = null;        try {            // 加载数据库驱动            Class.forName(JDBC_DRIVER);            // 连接数据库            conn = DriverManager.getConnection(DB_URL, USER, PASS);            // 执行SQL查询            stmt = conn.createStatement();            String sql = "SELECT id, age, first, last FROM Employees";            rs = stmt.executeQuery(sql);            // 遍历结果集            while (rs.next()) {                int id = rs.getInt("id");                int age = rs.getInt("age");                String first = rs.getString("first");                String last = rs.getString("last");                System.out.printf("%d,%d,%s,%s", id, age, first, last);            }        } catch (Exception e) {            e.printStackTrace();        } finally {            // 释放数据库资源            try {                if (rs != null) {                    rs.close();                }            } catch (SQLException e) {                e.printStackTrace();            }            try {                if (stmt != null) {                    stmt.close();                }            } catch (SQLException e) {                e.printStackTrace();            }            try {                if (conn != null) {                    conn.close();                }            } catch (SQLException e) {                e.printStackTrace();            }        }    }

注：该代码已被优化，主要改动包括：

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